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Methanogenesis in late Pleistocene permafrost sediments of the Lena Delta, Siberia

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Citation:
Wagner, D. , Kurchatova, A. and Gattinger, A. (2004): Methanogenesis in late Pleistocene permafrost sediments of the Lena Delta, Siberia , International Workshop on Geomicrobiology, Aarhus, DenmarkJanuary 2004. .
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Abstract:

Tundra environments of the Arctic are natural sources of methane, which is one of the most important climate-relevant trace gases. In polar regions huge layers of frozen ground are formed termed permafrost which covers more than 20 % of the land surface. The permafrost thickness can reach several hundreds of meters, e.g. in northeast Siberia about 600 800 m. During the relatively short period of Arctic summer only the surface zone (active layer) of permafrost thaws.Permafrost is colonized by high numbers of chemoorganotrophic bacteria as well as of microbes like highly specialized methanogenic archaea. Viable cells were found in geological horizons up to 3 million of years.In order to improve our understanding of the carbon dynamic and budget for the Lena Delta region (N 72°22, E 126°28) the methane fluxes as well as the processes, diversity and physiology of the microbial community have to be addressed not only in the active layer but also in the underlying frozen permafrost deposits. Therefore permafrost cores of Holocene and late Pleistocene age were drilled and transported in frozen conditions to Germany for microbiological, molecular ecological and geochemical analysis.The permafrost sediments are characterized by silty material with a high ice content between 11 and 35 %. The organic carbon of the core material varied between 0.6 and 4.9 %. In all permafrost deposits a high CH4 and CO2 concentration were proven and methanogenesis could be initiated after thawing of the sediment. Even the incubation of soil material at 3 °C (0.1 11.4 nmol CH4 h-1 g-1) and 6 °C (0.08 4.3 nmol CH4 h-1 g-1) showed a significant CH4 production. Phospholipid etherlipid (PLEL) analysis showed a high amount of archaeal biomass in permafrost layers with high concentrations of methane.The results indicated the existence of a permafrost microbiota, which has well adapted to the extreme environmental conditions. Furthermore, first evidence of modern methanogenesis in the perennially frozen sediments was given by microbial activity and PLEL analysis. The characterization of pure cultures of methanogenic archaea obtained from permafrost habitats should deliver detailed information of metabolic activity and survival potential of the microorganisms.

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